The branch control on user and consumed-steering bubbles could enable
only when a completed turn ended with no node after the message at all,
so readers saw a permanently unavailable control whose tooltip promised
a state it could not reach. An enabled one would mislead anyway: a fork
at a message seq cuts at the containing turn/end and takes the answer
along, the opposite of the branch-to-re-ask reading a control on one's
own bubble suggests.
MessageItem loses its fork props, PendingSteeringBubble loses the
showBranch special case, and messageBranchSeqs narrows to
assistantBranchSeqs: only a completed turn's transcript tail that is
the turn's own content-text assistant may fork. A steered turn keeps
its fork point under the settled answer, because fork is a log-prefix
cut and the steer is model-visible history the child inherits.
Web aria goldens drop the user-bubble disabled-branch row and its
hidden explanation text; the nested-subagent golden also loses the one
enabled user-tail fork handle, a loss the decision note accepts.
The user bubble's IconActions row carried an edit button with no click
handler, no client mutation, and no host operation behind it, advertising
an affordance the product cannot honor. The row now renders clock / copy /
branch only for both user and assistant chrome, and MessageIconActions
loses the `edit` prop with the button.
The package README records the missing capability under Known Limitations,
the web aria goldens pin the row without the control, and the Agent Note
states what must exist before it comes back.
